Under-sea oil storage installation

ABSTRACT

An installation including first and second storage tanks supported on the sea bottom; the second or external tank may be annular in shape and surround the first, or internal tank. Means are provided for introducing oil into and removing oil from, the upper part of the internal tank, and conduit means establish communication between the lower part of the internal tank and the upper part of the external tank. The external tank has openings at its bottom through which it communicates with the sea, and a roof having an arched cross-sectional shape. The outer wall of the internal tank may form the inner wall of the external tank and support a hollow shaft extending above the sea surface, the shaft carrying an equipment-supporting platform. Within the internal tank is a sludge-gathering means, which may be perforated plates or netting, for directing sludge into a deposit tank. Means are provided for agitating the sludge preparatory to its being pumped out of the deposit tank.

Hirata UNDER-SEA OIL STORAGE INSTALLATION 1451 Aug. 21, 1973 Primary Examiner-Samih N. Zaharna Assistant Examiner-T. A. Granger 76 l t H hlIIi ta l-302-h 1 men or 1: i Tokyo z zfi Attorney-Bre1tenfeld & Levine [22] Filed: Sept. 14, 1971 [57] ABSTRACT [21] Appl. No.: 180,293 An installation including first and second storage tanks supported on the sea bottom; the second or external tank may be annular in shape and surround the first, or [30] Fme'gn Apphcamm Pnomy internal tank. Means are provided for introducing oil Dec. 15, 1970 Japan 45/1 1 l 157 into and removing n from, the upper part of the inter nal tank, and conduit means establish communication [52] US. CL. 210/170, 114/.5 T between the lower part of the internal tank and the [51] lift. CI E02b /04 upper p f h external tank The external tank has [58] Field of Search 166/5, .6; 137/136; openings at its bottom through which it communicates 114/.5 T; 210/83, 242, DIG. 21, 170, 525. 524 with the sea, and a roof having an arched crosssectional shape. The outer wall of the internal tank may {56] References C'ted form the inner wall of the external tank and support a UNITED STATES PATEN S hollow shaft extending above the sea surface, the shaft 3,339,512 9/1967 Siegel.... 210/D1G. 21 carrying an equipment-supporting platform. Within the 3,408,971 11/1968 Mott 114/.5 T internal tank is a sludge-gathering means, which may 2,377,875 6/1945 Geisslel' 210/525 X be perforated plates or netting, for directing sludge into 3 1 3/1944 F 210/524 X a deposit tank. Means are provided for agitating the 2 ilegel sludge preparatory to its being pumped out of the deogonows l posit tank.

15 Claims, 7 Drawing Figures e 25/ A 242 26H run-'7 Z 5 43 J I: T M 1 i i 1 s 37 i i 3 E A9 46' I L 3/ /Z ,0 LT 5 0/ r T Z A? 0 I lvtyo I i 5 a //0 i l M I a 1 i f 1/ g 1 I i i m T t 5 JR g Y I 1... 1 1. 1 33 I E 1 I j 1-51, 7 4 II V 11 III; II I/ PATENTEI] AUG 2 1 I875 sum 2 or 4 1N VENTOR: H/AOSH/ H/AurA UNDER-SEA OIL STORAGE INSTALLATION This invention is concerned with under-sea tanks in which crude oil or petroleum oil products (hereinafter referred to as oil) are stored.

When crude oil is removed from an off-shore oil well, the conventional method of transporting the crude oil from the production well to an oil refinery is as follows: the crude oil is transported by a submerged pipe line from the well to tanks constructed on the land near the wells, and stored in the tanks. If the oil is then to be loaded into a tanker, it is pumped from the storage tanks through a land pipe line to the tanker.

In the conventional arrangement described above, many facilities must be provided together with the storage tanks, such as pumps, generator pipe lines, submerged pipe lines, moorings, many foundations, fire extinguishers, a pump house, roads, offices, employee housing, land. The cost of constructing these facilities is high, as is the cost of maintaining the facilities and personnel. Should the production of crude oil from underground decrease after all the facilities mentioned above have been constructed, the facilities will not be used to full capacity, and cannot be used elsewhere, and hence can become very uneconomic.

Some research and development concerning undersea storage tanks has been done, with the idea of saving the expense of installing much of the equipment mentioned above. However, construction of such tanks, dispersion of sludge included in the oil, and operation of the oil storage and discharge in connection with such tanks, have presented many problems.

It is an object of the present invention to provide a practical under-sea oil storage installation which does not present the problems heretofore faced by such installations.

According to the preferred embodiment of the present invention, the installation includes an external tank having an annular shape, and an arched circular roof, the external tank surrounding an internal tank formed with a frusto-conical roof. The internal wall of the external tank forms the external wall of the internal tank.

Oil is introduced into, and removed from, the upper part of the internal tank. Conduit means connect the lower part of the internal tank with the upper part of the external tank, and openings are provided in the lower portion of the exterior wall of the external tank, sea water flowing into and out of the external tank through these openings.

A hollow shaft is mounted on the roof of the internal tank, and an equipment-supporting platform is carried by the shaft above the sea surface. Spokes are provided which extend radially between the internal and external walls of the external tank, so as to maintain the walls concentric.

Perforated plates or nets are provided in the internal tank to catch the sludge carried by the oil, and deposit the sludge in a deposit tank at the bottom of the internal tank.

When there is a small quantity of oil stored in the installation described above, the external tank is completely filled with sea water, and the internal tank is almost completely filled with sea water. However, some oil will remain above the sea water in the internal tank. As oil is pumped into the internal tank, it does not mix with the sea water, but instead pushes the sea water downwardly in the internal tank. The sea water then flows through the conduit means into the upper portion of the external tank, and finally out through the openings at the bottom of the external tank. As oil continues to be pumped, it flows through the conduit means into the upper portion of the external tank, continuing to push the sea water out below it. Pumping continues until the bottom level of the oil almost reaches the openings at the bottom of the external tank. When oil is pumped out of the internal tank, it flows through the conduit means between the internal and external tanks, into theinternal tank, and as oil leaves the external tank, sea water flows in to take its place. Pumping of the oil out of the internal tank continues until the level of the sea water in the internal tank almost reaches the pumping means, at which point pumping is stopped. Thus, the storage tanks are always filled with a combination of oil and sea water, although of course these two materials are not mixed.

Since the sludge is collected in a deposit tank at the bottom of the internal tank, it never reaches the external tank, and therefore does not flow out of the external tank and pollute the sea. As oil is being discharged from the internal tank, a portion of the oil is directed as a jet into the sludge, to agitate the latter, and the mixed oil and sludge are blended. The deposit tank may also be provided with rotating blades to further agitate and liquify the sludge. The liquified sludge is then pumped out of the deposit tank.

As mentioned above, oil enters the external tank at the top of the tank, while sea water leaves the external tank at the bottom of the tank. This arrangement, coupled with the fact that little or no sludge is allowed to enter the external tank, greatly minimizes or eliminates pollution of the surrounding sea.

Additional objects and features of the present invention will be apparent from the following description, in which reference is made to the accompanying drawings.

In the drawings:

FIG. 1 is a vertical cross-sectional view of an undersea oil storage installation according to the present invention;

FIG. 2 is a horizontal cross-sectional view taken along line 2-2 of FIG. 1; 7

FIG. 3 is a schematic illustration of the installation showing the direction of oil flow therein;

FIG. 4 is a view similar to FIG. 1 of an alternative embodiment of the present invention;

FIG. 5 is a horizontal cross-sectional view taken along line 5-5 of FIG. 4;

FIG. 6 is a view similar to FIG. 1 of another alternative embodiment of the present invention; and

FIG. 7 is a horizontal cross-sectional view taken along line 7-7 of FIG. 6.

FIGS. 1, 2, and 3 show an under-sea oil storage tank according to the present invention installed on a sea bottom 33. The installation includes an annular external tank 1 surrounding an internal tank 2. A hollow shaft 3, coaxial with tanks 1 and 2, projects upwardly above the sea surface and carries a platform 4.

External tank 1 comprises an external circular wall 1', an internal circular wall 5 coaxial therewith, and a circular arched roof 12 joining the upper edges of the two walls. lntemal wall 5 is common to both external tank 1 and the internal tank 2. The bottom of external tank 1 is equipped with a plurality of radiating spokes 9 each of which is provided with a turnbuckle 8, the

turnbuckles being adjustable to keep external wall 1' circular and concentric with internal wall 5. The ends of spokes 9 are fixed in the foundation 7 of external wall 1 and the foundation 6 of internal wall 5. External wall 1 is provided along its lower edge with a plurality of spaced-apart openings 11, and internal wall is similarly provided along its lower edge with a plurality of spaced-apart openings 13.

Internal wall 5 is seated upon the edge of the circular bottom plate 14 of internal tank 2. Flow pipes 10 establish communication between each opening 13 and the upper part 10 of external tank 1.

Within internal tank 2 is a series of vertically spacedaparat parallel plates 16. These plates serve to gather sludge which floats on the oil deposited in the tank. Each plate 16 is formed with a large number of holes 17. Each plate 16 slopes from its outer edge toward its center. As a result, sludge deposited on the plates flows toward the center of each plate and downwardly through a pipe 18 into a tank 15. Although plates 16 gather sludge for deposit in tank 15, oil is free to flow through the holes 17 in plates 16.

Mounted on the upper 'edge of wall 5 is a frustoconical roof 45, the upper edge of which carries hollow shaft 3. Connected in the side wall of hollow shaft 3 are valves 46 and 46 through which the interior of shaft 3 communicates with an oil receiving pipe 35. Fixed to the upper part of hollow shaft 3, above the sea surface 32, is the platform 4. Mounted on platform 4 is a motor 20 for driving an oil discharging pump 19. When pump 19 is operated, discharged oil is transferred to a tanker 38 (FIG. 3) through a flow meter 36 and a discharge pipe 37.

Part of the oil discharged by pump 19 reaches a branch pipe 26 before it arrives at flow meter36. A circulation pump 25 moves this oil portion through a pipe 27 which terminates at its lower end at the bottom of sludge deposit tank 15. The oil leaves pipe 27 as a jet 27' which agitates the sludge and causes it to float. Lof cated at the bottom of tank is the lower end 21 of a suction pipe 21'. The upper end of suction pipe 21 is connected to a water discharging pump 22, the sea water at the bottom of internal tank 2 is removed by operation of pump 22. Water discharge by pump 22 is stored in an oil and water separater 23 wherein oil is recovered. The recovered oil flows through pipe 43 into hollow shaft 3 and is stored in internal tank 2. After separation, pure sea water is discharged into the sea through pipe 24, flow through which is controlled by a valve 24.

The basic parts of the oil storage tank of this invention have been described above, and the operation is as follows:

Oil to be stored in the under-sea tank flows from oil receiving pipe 35 through valves 46 and 46, and in hollow shaft 3. Since the specific gravity of oil is lower than that of sea water, initially the oil remains in the upper part of hollow shaft 3, Le, near the height of the sea surface 32.

As the quantity of oil received increases, the sea water in hollow shaft 3 and internal tank 2 is pushed downwardly, and it flows out through openings 13 in internal wall 5. The water then flows through pipes 10 into external tank 1, and from this tank flows out to the sea through openings 11 in the lower part of external wall 1. When the received oil passes through the holes 17 in plates 16, low velocity parallel streams of oil are produced which move downwardly in the same direction as the sludge which is gathered and deposited as described above. As oil continues to be received, the lower surface of the oil falls to the height of openings 13 and begins to flow into external tank 1 through pipe 10. At the same time, electric current to oil surface indicator 40 (FIG. 3) is cut OK so that the control room 34 is informed of the location of the lower oil surface. Automatically, water discharging pump 22 is operated, and the sea water remaining beneath the level of openings 13 in internal tank 2 is drawn into suction plate 21 by water discharging pump 22. This pumping continues until the oil surface reaches oil surface indicator 42, and the pumped sea water is stored in oil and water separater 23. The separated oil is stored in hollow shaft 3, after flowing through pipe 43, and the separated sea water is discharged into the sea through valve 24' and discharging pipe 24. It will be seen that operation of discharging pump 22 causes oil to fill the lower part of internal tank 2, the oil replacing the discharged sea water.

As oil continues to be received, it fills external tank 1, and the lower oil surface continues to fall. When this oil surface reaches the level 30 (FIG. 1), the oil storage tank of the present invention has reached its full storage capacity. At this point, electric current to oil surface indicator 41 is cut off, to inform the control room 34, and pumping of oil to the storage tank is discontinued.

When stored oil is to be discharged, motor 20 is energized to operate oil discharging pump 19. The pump is located so as to be deeper than the valley of the largest wave when the tide is out. At the beginning of the discharging operation, a portion of the discharging oil is delivered to the bottom of tank 15 by pump 25. As a result, the sludge in tank 15 is agitated and the oil and the sludge are delivered to an oil tanker receiving oil from the undersea tank. As oil is discharged to the tanker, an equal amount of sea water flows into external tank 1 through openings 1 1. As sea water fills external tank 1, the oil above it flows through pipe 10 into internal tank 2.

When all the oil in external tank 1 has flowed into internal tank 2, sea water begins to flow into internal tank 2 through pipe 10. When the sea water surface reaches the level of oil surface indicator 42, control room 34 is informed of this, and automatically circulation pump 25 stops operating so that the oil and the sea water are not mixed. As oil continues to be discharged, the sea water surface reaches the level 31, and this is sensed by oil surface indicator 39. As a result, motor 20 operating pump 19 automatically stops operating, and discharge of oil terminates.

A vent pipe 28, equipped with a fire extinguisher 29, is mounted on the upper part of hollow shaft 3. Gas within hollow shaft 3 is safely exhausted through vent pipe 28.

The alternative under sea oil storage tank shown in FIGS. 4 and 5 is identical to the one shown in FIGS. 1-3, except that the tank of FIGS. 4 and 5 is not equipped with plates 16 upon which sludge is deposited. Sludge deposited in tank 15 at the bottom of internal tank 2 is floated by operation of pump 25 which produces a circulating jet of oil. Floatation of the sludge is aided by rotating blades 47. Another difference in the tank of FIGS. 4 and 5 is the provision of columns 48 for supporting platform 4, the columns being mounted on the upper part of the internal wall 5. Platform 4 must have a large surface area, so as to support big equipment, and it must be stomg enough to bear up against the effects of waves and wind. Strong and heavy materials are necessary for constructing the platform, and this is expensive. By providing columns 48 for supporting platform 4, it is possible to construct hollow shaft 3 with light weight materials.

The embodiment of the invention shown in FIGS. 6 and 7 is identical to that of FIGS. 1-3, except that in place of plates 16, the arrangement of FIGS. 6 and 7 employs within internal tank 2 a netting 49. The netting may be arranged in the form of a plate, or it may be hung to form concentric cylinders. The equipment for agitating and floating the sludge is the same as shown in FIG. 4, and the mechanism for storing and discharging the oil is the same as in FIG. 1. In addition, columns 48, as described above in connection with FIG. 4, are employed.

Since the undersea tank of the present invention will receive the effects of billow, sea tide, and wind pressure, tending to move it horizontally, suitable stakes, or like abutments, should be driven into the sea bottom around the outside circumference of external tank 1, or the bottom of the external tank should be concreted or surrounded with large rocks. Furthermore, the undersea tank will be subjected to a force tending to float it resulting from the difference in specific gravities of the oil and sea water. Therefore, the tank body must be weighted to resist this force, or staked.

With the present invention, oil flows from the bottom of the internal tank into the external tank, and during this flow through the internal tank, sludge carried by the oil is deposited in the internal tank and can then be pumped out without polluting the sea. A sludge is removed from the internal tank at the same time oil is discharged, and hence depositing the sludge at the bottom of the internal tank presents no problem.

The circular arched shape of the roof 12 of external tank 1 has been found best for resisting the force mentioned above produced by the difference of specific gravities of the oil and sea water, and for resisting the force of waves in the sea when no oil is stored in the external tank. Under certain circumstances, such is when the volume of external tank 1 is large, spokes 9 may be replaced by prestressed concrete beams.

I claim:

1. An under-sea oil storage installation comprising:

first and second storage tanks supported on the sea bottom,

means for introducing oil into the upper part of said first tank and for removing oil therefrom,

conduit means through which the lower part of said first tank communicates with the upper part of said second tank,

an opening in the lower part of said second tank through which the interior of said second tank communicates with the sea, sea water being free to flow into said tank through said opening, and

a sludge deposit tank within said first tank and sludge-gathering means within said first tank for accumulating and depositing sludge carried by the oil in said deposit tank, said sludge-gathering means allowing the oil to flow through it, whereby when said tanks are empty of oil they are filled with sea water, but when oil is pumped into said first tank it first fills the latter and upon continued pumping flows sludge-free through said conduit means into said second tank, the sea water being pushed by the oil out of said tanks through said opening, and when oil is pumped out of said first tank sea water flows into said tank through said opening pushing oil out of said second tank through said conduit means into said first tank.

2. An under-sea oil storage installation as defined in claim 1 wherein said second storage tank has an annular shape and surrounds said first storage tank.

3. An under-sea oil storage installation as defined in claim 2 including a circular roof covering said second tank, said roof having an arched cross-sectional shape.

4. An under-sea oil storage installation as defined in claim 2 wherein said second tank has inner and outer concentric walls, and including rigidifying spokes extending radially between said walls, the ends of each spoke being fixed to said inner and outer walls respectively.

5. An under-sea oil storage installation as defined in claim 2 wherein said second tank has inner and outer concentric walls, said inner wall serving also as the side wall of said first tank.

6. An under-sea oil storage installation as defined in claim 5 including an equipment-supporting platform above said storage tanks, and columns supported on said inner wall supporting said platform.

7. An under-sea oil storage installation as defined in claim 1 including a hollow shaft supported on said first tank, the upper end of said shaft extending above the sea surface and the interior of said shaft communicating with the interior of said first tank, and said oil introducing and removing means being located within said shaft.

8. An under-sea oil storage installation as defined in claim 7 including an equipment-supporting platform carried by said shaft above the sea surface.

9. An under-sea oil storage installation as defined in claim 1 wherein said sludge-gathering means includes at least one perforated plate.

10. An under-sea oil storage installation as defined in claim 9 wherein said sludge-gathering means are above said deposit tank, and including a pipe between said sludge gathering means and said deposit tank, said pipe having a first opening communicating with said plate, and a second opening communicating with said deposit tank, and siad plate being shaped to slope toward said first opening of said pipe.

11. An under-sea oil storage installation as defined in claim 1 wherein said sludge-gathering means includes a net.

12. An under-sea oil storage installation as defined in claim 1 including a pump for discharging the contents of said deposit tank.

13. An under-sea storage installation as defined in claim 12 including means for diverting a portion of the oil being discharged from said first tank into said deposit tank, said diverting means introducing oil into said deposit tank in the form of a jet for agitating the sludge therein.

14. An under-sea oil storage installation as defined in claim 12 including blades within said deposit tank, and means for rotating said blades to agitate the sludge.

15. An under-sea oil storage installation as defined in claim 12 including an oil and water separator, said pump discharging the contents of said deposit tank into said separator.

* i i i 

1. An under-sea oil storage installation comprising: first and second storage tanks supported on the sea bottom, means for introducing oil into the upper part of said first tank and for removing oil therefrom, conduit means through which the lower part of said first tank communicates with the upper part of said second tank, an opening in the lower part of said second tank through which the interior of said second tank communicates with the sea, sea water being free to flow into said tank through said opening, and a sludge deposit tank within said first tank and sludgegathering means within said first tank for accumulating and depositing sludge carried by the oil in said deposit tank, said sludge-gathering means allowing the oil to flow through it, whereby when said tanks are empty of oil they are filled with sea water, but when oil is pumped into said first tank it first fills the latter and upon continued pumping flows sludge-free through said conduit means into said second tank, the sea water being pushed by the oil out of said tanks through said opening, and when oil is pumped out of said first tank sea water flows into said tank through said opening pushing oil out of said second tank through said conduit means into said first tank.
 2. An under-sea oil storage installation as defined in claim 1 wherein said second storage tank has an annular shape and surrounds said first storage tank.
 3. An under-sea oil storage installation as defined in claim 2 including a circular roof covering said second tank, said roof having an arched cross-sectional shape.
 4. An under-sea oil storage installation as defined in claim 2 wherein said second tank has inner and outer concentric walls, and including rigidifying spokes extending radially between said walls, the ends of each spoke being fixed to said inner and outer walls respectively.
 5. An under-sea oil storage installation as defined in claim 2 wherein said second tank has inner and outer concentric walls, said inner wall serving also as the side wall of said first tank.
 6. An under-sea oil storage installation as defined in claim 5 including an equipment-supporting platform above said storage tanks, and columns supported on said inner wall supporting said platform.
 7. An under-sea oil storage installation as defined in claim 1 including a hollow shaft supported on said first tank, the upper end of said shaft extending above the sea surface and the interior of said shaft communicating with the interior of said first tank, and said oil introducing and removing means being located within said shaft.
 8. An under-sea oil storage installation as defined in claim 7 including an equipment-supporting platform carried by said shaft above the sea surface.
 9. An under-sea oil storage installation as defined in claim 1 wherein said sludge-gathering means includes at least one perforated plate.
 10. An under-sea oil storage installation as defined in claim 9 wherein said sludge-gathering means are above said deposit tank, and including a pipe between said sludge gathering means and said deposit tank, said pipe having a first opening communicating with said plate, and a second opening communicating with said deposit tank, and siad plate being shaped to slope toward said first opening of said pipe.
 11. An under-sea oil storage installation as defined in claim 1 wherein said sludge-gathering means includes a net.
 12. An under-sea oil storage installation as defined in claim 1 including a pump for discharging the contents of said deposit tank.
 13. An under-sea storage installation as defined in claim 12 including means for diverting a portion of the oil being discharged from said first tank into said deposit tank, said diverting means introducing oil into said deposit tank in the form of a jet for agitating the sludge therein.
 14. An under-sea oil storage installation as defined in claim 12 including blades within said deposit tank, and means for rotating said blades to agitate the sludge.
 15. An under-sea oil storage installation as defined in claim 12 including an oil and water separator, said pump discharging the contents of said deposit tank into said separator. 